A base transceiver station for radio communications exchanges control data with a mobile station to communicate therewith, and uses the control data to control the communication. When the control data is transmitted/received in an encoded state, the base transceiver station decodes the control data transmitted from the mobile station.
FIG. 1 is diagram illustrating one example of processing for decoding control data. FIG. 1 illustrates an example in which control data transmitted from a mobile station is a channel quality indicator (CQI) value indicative of a data reception quality of the mobile station and a base transceiver station decodes the CQI value by using a correlation detection method. Upon receiving the encoded CQI value from the mobile station, the base transceiver station performs correlation calculation for comparing received data with sequences (candidate sequences) that serve as candidates for an encoded sequence indicating information having a possibility of being transmitted as the CQI value. Thereafter, the base transceiver station performs decoding using a result of the correlation calculation and determines a reliability of the decoding result. When the determined reliability exceeds a certain threshold, the base transceiver station determines that the decoding was correctly performed.
The control data is used to control communication. Thus, when the control data is erroneously decoded, the communication efficiency may decline. Accordingly, it is desirable that correctly decoded data be used as the control data. Performing control using successfully decoded control data is desirable not only in the exemplary case illustrated in FIG. 1 but also in any communication in which encoded control data is transmitted/received.
One known decoding method using a correlation detection method is a method involving a process of determining a decoding reliability of a decoding result by using one or multiple correlation values obtained during correlation calculation and a process of correcting the decoding result based on the decoding reliability (refer to Japanese Laid-Open Patent Publication No. 2006-203843). As a related technology, for example, a communication device having a bitwise likelihood calculating unit for calculating a likelihood for each bit contained in an estimated transmission symbol and a receiver having a decoder for decoding a transmitted bit sequence by using a bitwise likelihood are known (e.g., refer to Japanese Laid-Open Patent Publication No. 2008-48219).
When controlled data that is not successfully decoded is used, the communication efficiency may decline. It is, therefore, desired that detection of a decoding error with respect to control data be performed with high accuracy.